Base station apparatus, terminal apparatus, transmitting method, and receiving method

ABSTRACT

Disclosed is a base station apparatus which allows an idle mode UE, in a small cell using S-NCT, to recognize the small cell and to receive a DCI. The base station apparatus is configured to use a carrier configuration which has no region for mapping a PDCCH and in which an EPDCCH is mapped in a data region. The base station apparatus includes: master information generating section  101  configured to generate allocation information indicating a resource which forms a search space in the EPDCCH and being scrambled with a cell ID of the base station apparatus; and transmitting section  107  configured to transmit the allocation information, a detection signal indicating the cell ID, and a control signal assigned in the search space.

BACKGROUND Technical Field

The present invention relates to a base station apparatus, a terminalapparatus, a transmitting method, and a receiving method.

Description of the Related Art

In recent years, it has become almost common to transmit not only speechdata but also large volume data such as still image data and movingimage data, along with the increasing adoption of multimedia-enabledinformation in cellular mobile communication systems. Meanwhile, studieshave been actively carried out to achieve a higher transmission-rateusing a wide radio band, multiple-input multiple-output (MIMO)transmission technology, and interference control technique in long-termevolution advanced (LTE-Advanced).

In addition, studies have been carried out to achieve a highertransmission rate at hotspots through the deployment of small cells,each being a base station using low transmission power (may be referredto as “eNB”) in a cellular mobile communication system in LTE-Advanced.In addition, allocating a frequency different from that for macro cellsas a carrier frequency for operating small cells has been under study(see Non-Patent Literature (hereinafter, abbreviated as “NPL”) 1).

In addition, operating small cells by using a carrier configurationcalled “New Carrier Type (NCT),” which is different from the carrierconfiguration used until LTE-Advanced Rel. 11 (i.e., Backward CompatibleCarrier (BCT), see FIG. 1A, for example), has been under discussion. InNCT, studies have been carried out on reducing a physical downlinkcontrol channel (PDCCH) and a cell specific reference signal (CRS)transmitted in BCT and using an enhanced PDCCH (EPDCCH) for transmissionof a downlink (DL) control signal and using a demodulation referencesignal (DMRS) for demodulation of a signal (see, FIG. 1B, for example).An EPDCCH is mapped in a data region, and the base station is capable ofspecifying a frequency resource and then transmitting the EPDCCH.Accordingly, the transmission using an EPDCCH enables controllingtransmission power for a control signal, or controlling interferencegiven to a different cell by the control signal to be transmitted, orcontrolling interference given to a cell of the base station from adifferent cell.

In addition, studies have been carried out on a situation whereterminals (UE: User Equipment) are connected to both a macro cell andsmall cell and also on a situation where UEs are connected to only asmall cell. The carrier to be used in a small cell in the situationwhere terminals (UE: User Equipment) are connected to both a macro celland small cell is called “Non-standalone-NCT (NS-NCT).” Meanwhile, thecarrier to be used in a small cell in the situation where UEs areconnected to only a small cell is called “standalone-NCT (S-NCT).”

When a UE connects to a small cell using NS-NCT, it is likely that theUE connects to a macro cell first and is then instructed by the macrocell to connect to the small cell using NS-NCT. Thus, small cells usingNS-NCT can perform processing to connect UEs with support from a macrocell.

Meanwhile, since small cells using S-NCT receive no support from a macrocell, the small cells themselves need to allow UEs to connect to thesmall cells. In addition, the small cells using S-NCT are expected tosupport not only connective mode UEs, but also idle mode UEs performingno data communication. The possibility of implementing thisconfiguration has been under discussion as well. To put it differently,the small cells each using S-NCT need to be configured to transmitinformation to idle mode UEs in order for the idle mode UEs to recognizethe presence of small cell (e.g., cell detection), when S-NCT is used.

In BCT in which a macro cell is put into operation, each idle mode UEperforms synchronization and cell detection using a primarysynchronization signal (PSS)/secondary synchronization signal (SSS).After acquisition of the cell ID of a macro cell, the idle mode UEreceives a master information block (MIB) and thereby acquires atransmission band, physical HARQ indicator channel (PHICH) mappinginformation, and a frame number and/or the like. Thereafter, the UEmonitors a common search space (CSS) on a PDCCH configured with a shiftpattern defined the cell ID, and blindly detects downlink controlinformation pieces (DCIs) on the system information, paging, and arandom access channel (RACH). The DCIs on the system information,paging, and RACH are masked with SI-RNTI, P-RNTI, and RA-RNTI or thelike, respectively. Note that, the eNB does not recognize that idle modeUEs monitor the cell provided by the eNB, so that the eNB cannottransmit information to the idle mode UEs, using a UE-specific controlsignal.

CITATION LIST Non-Patent Literatures

-   NPL 1-   3GPP TR 36.872 V0.3.0, “Small Cell Enhancements for E-UTRA and    E-UTRAN Physical Layer Aspects”-   NPL 2-   R1-121193, “Summary of email discussion on CSS for ePDCCH,” Fujitsu

BRIEF SUMMARY Technical Problem

As in BCT, in a small cell using S-NCT, a system is also needed, whichallows an idle mode UE to recognize the small cell and to receive theDCIs on the system information, paging, and RACH. However, as describedabove, no PDCCH is transmitted in NCT (see FIG. 1B). For this reason, inNCT, a CSS needs to be configured on an EPDCCH (hereinafter, referred toas “EPDCCH-CSS”) to allow UEs to receive the DCIs on the systeminformation, paging, and RACH on the EPDCCH-CSS. In this configuration,the EPDCCH-CSS needs to be configured so as to allow UEs to recognizethe EPDCCH-CSS without a UE-specific control signal and to monitor theEPDCCH-CSS. In addition, a system that allows idle mode UEs to acquirethe RB number and the number of RBs to which the EPDCCH is mapped.Providing a CSS in EPDCCH has been studied once in BCT in Rel. 11 (seeNPL 2), but it has been decided not to introduce a CSS in EPDCCH in Rel.11. In this study, providing a CSS in EPDCCH has been discussed with theassumption that the EPDCCH CSS is mainly targeted for connected UEs andalso that the resources for the EPDCCH CSS are indicated by higher layersignaling.

It is an object of the present invention to provide a base stationapparatus, a terminal apparatus, a transmitting method, and a receivingmethod each allowing, in a small cell using S-NCT, an idle mode UE torecognize the small cell and thereby to receive a DCI.

Solution to Problem

A base station apparatus according to an aspect of the present inventionis a base station apparatus using a carrier configuration which includesno region for mapping a physical downlink control channel (PDCCH) and inwhich an enhanced physical downlink control channel (EPDCCH) is mappedin a data region, the base station apparatus including: a generatingsection that generates allocation information indicating one or moreresources which form a search space in the EPDCCH and being scrambledwith a cell ID of the base station apparatus; and a transmitting sectionthat transmits the allocation information, a detection signal indicatingthe cell ID, and a control signal assigned in the search space.

A terminal apparatus according to an aspect of the present inventionincludes: a detection section that detects a detection signal from areceived signal transmitted from a base station apparatus using acarrier configuration which includes no region for mapping a physicaldownlink control channel (PDCCH) and in which an enhanced physicaldownlink control channel (EPDCCH) is mapped in a data region, thedetection signal indicating a cell ID of the base station apparatus; afirst receiving section that extracts allocation information from thereceived signal, using the cell ID, the allocation informationindicating one or more resources which form a search space in theEPDCCH; and a second receiving section that extracts a control signalfrom the received signal by performing blind-decoding with respect tothe search space.

A transmitting method according to an aspect of the present invention isa transmitting method in a base station apparatus using a carrierconfiguration which includes no region for mapping a physical downlinkcontrol channel (PDCCH) and in which an enhanced physical downlinkcontrol channel (EPDCCH) is mapped in a data region, the transmittingmethod including: generating allocation information indicating one ormore resources which form a search space in the EPDCCH and beingscrambled with a cell ID of the base station apparatus; and transmittingthe allocation information, a detection signal indicating the cell ID,and a control signal assigned in the search space.

A receiving method according to an aspect of the present inventionincludes: detecting a detection signal from a received signaltransmitted from a base station apparatus using a carrier configurationwhich includes no region for mapping a physical downlink control channel(PDCCH) and in which an enhanced physical downlink control channel(EPDCCH) is mapped in a data region, the detection signal indicating acell ID of the base station apparatus; extracting allocation informationfrom the received signal, using the cell ID, the allocation informationindicating one or more resources which form a search space in theEPDCCH; and extracting a control signal from the received signal byperforming blind-decoding with respect to the search space.

Advantageous Effects of Invention

According to the present invention, in a small cell using S-NCT, an idlemode UE can recognize the small cell and receive a DCI.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1A is a diagram illustrating a BCT carrier configuration, and FIG.1B is a diagram illustrating an NCT carrier configuration;

FIG. 2 is a block diagram illustrating a primary configuration part of abase station according to Embodiment 1 of the present invention;

FIG. 3 is a block diagram illustrating a primary configuration part of aterminal according to Embodiment 1 of the present invention;

FIG. 4 is a block diagram illustrating a configuration of the basestation according to Embodiment 1 of the present invention;

FIG. 5 is a block diagram illustrating a configuration of the terminalaccording to Embodiment 1 of the present invention;

FIG. 6 is a diagram illustrating a correspondence between thetransmission bandwidth and the number of RBs of EPDCCH CSS according toEmbodiment 1 of the present invention;

FIG. 7 is a diagram illustrating a mapping example of an EPDCCH CSSaccording to Embodiment 1;

FIG. 8 is a diagram illustrating an EPDCCH CSS mapping method accordingto a variation of Embodiment 1 of the present invention;

FIG. 9 is a diagram illustrating an EPDCCH CSS mapping method accordingto another variation of Embodiment 1 of the present invention;

FIG. 10 is a block diagram illustrating a configuration of a basestation according to Embodiment 2 of the present invention;

FIG. 11 is a block diagram illustrating a configuration of a terminalaccording to Embodiment 2 of the present invention;

FIG. 12 is a diagram illustrating an EPDCCH CSS mapping method in eachsubframe according to Embodiment 2 of the present invention (OperationExample 1);

FIG. 13 is a diagram illustrating another EPDCCH CSS mapping method ineach subframe according to Embodiment 2 of the present invention(Operation Example 2);

FIG. 14 is a diagram illustrating still another EPDCCH CSS mappingmethod according to Embodiment 2 of the present invention (OperationExample 3);

FIG. 15 is a diagram illustrating the EPDCCH CSS mapping method in eachsubframe according to Embodiment 2 of the present invention (OperationExample 3); and

FIG. 16 is a diagram illustrating the EPDCCH CSS mapping methodaccording to Embodiment 2 of the present invention (Operation Example3).

DETAILED DESCRIPTION

Hereinafter, each embodiment of the present invention will be describedin detail with reference to the accompanying drawings. In describing theembodiments, the same configuration elements are assigned the samereference numerals, and redundant descriptions of the configurationelements will be omitted.

Embodiment 1

[Configuration of Communication System]

A communication system according to Embodiment 1 is an LTE-Advancedsystem, for example, and includes base station 100 and terminal 200.Base station 100 is a small cell supporting the LTE-Advanced system, forexample. Terminal 200 is a terminal supporting the LTE-Advanced systemand is connected only to base station 100 (small cell). Specifically,base station 100 and terminal 200 use S-NCT (hereinafter, may bereferred to as “NCT,” simply).

Base station 100 maps an EPDCCH-CSS in NCT and transmits DCIs on thesystem information, paging and RACH, using the EPDCCH-CSS. In thistransmission, base station 100 indicates, to terminal 200, resourceallocation information for identifying the start position of and thenumber of RBs to which the EPDCCH-CSS is mapped, by an NCT-MIB (MIBmapped in NCT). The RB to which the NCT-MIB is mapped may be configuredto be shared by all the cells as in BCT or may be determined on thebasis of the cell ID of the small cell (base station 100). In addition,the NCT-MIB is subjected to scrambling processing on the basis of thecell ID of the small cell.

In addition, studies have been carried out on using, as a detectionsignal (discovery signal) or synchronization signal, PSS/SSS, CRS,CSI-RS, PRS, or a signal to be newly designed, in NCT, while a PSS/SSSis used in detection and synchronization with a cell by terminals inBCT. In NCT, whether or not to perform only cell detection under theassumption that the terminal has already been in synchronization withthe base station, or to perform not only cell detection but alsosynchronization with the cell depends on the design of cell. In thisembodiment, however, no particular distinction is made between thedetection signal (discovery signal) and synchronization signal, and thetwo signals are combined together and called a “discovery signal.”

Embodiment 1 will be described regarding a case where the cell ID can beidentified by a discovery signal in terminal 200. However, the cell IDmay be previously indicated to terminal 200 by a neighboring cell or thelike. Terminal 200 demodulates the NCT-MIB using a DMRS of the RB towhich the NCT-MIB is mapped, or the cell ID indicated by the discoverysignal.

[Primary Configuration Part of Base Station 100]

FIG. 2 is a block diagram indicating a primary configuration part ofbase station 100 according to Embodiment 1. Base station 100 uses acarrier configuration (NCT) which includes no PDCCH region for mapping aPDCCH and in which an EPDCCH is mapped in a data region. In base station100, master information generating section 101 generates allocationinformation which indicates the resources forming a search space (EPDCCHCSS) in an EPDCCH and which is scrambled with the cell ID of basestation 100. Signal assignment section 106 assigns the allocationinformation and the discovery signal indicating the cell ID to thecorresponding resources and assigns a control signal (DCI) in the searchspace. In this manner, the allocation information, the discovery signalindicating the cell ID and the control signal (DCI) that has beenassigned in the search space are transmitted.

[Primary Configuration Part of Terminal 200]

FIG. 3 is a block diagram illustrating a primary configuration part ofterminal 200 according to Embodiment 1. In terminal 200, signaldemultiplexing section 202 receives a received signal transmitted frombase station 100 that uses a carrier configuration (NCT) which includesno region for mapping a PDCCH and in which an EPDCCH is mapped in a dataregion. Discovery signal detecting section 205 detects a discoverysignal indicating the cell ID of base station 100 from the receivedsignal. Master information receiving section 206 extracts the allocationinformation indicating the resources forming a search space in theEPDCCH from the received signal using the abovementioned cell ID. Commoncontrol signal receiving section 207 extracts a control signal (DCI)from the received signal by performing blind-decoding with respect tothe search space.

[Configuration of Base Station 100]

FIG. 4 is a block diagram illustrating a configuration of base station100 according to Embodiment 1 of the present invention.

Referring to FIG. 4, base station 100 includes master informationgenerating section 101, discovery signal generating section 102, commoncontrol signal generating section 103, error correction coding section104, modulation section 105, signal assignment section 106, transmittingsection 107, receiving section 108, demodulating section 109, and errorcorrection decoding section 110.

Master information generating section 101 generates control informationto be transmitted as an MIB (NCT-MIB) to be mapped in NCT. Masterinformation generating section 101 outputs the generated NCT-MIB toerror correction coding section 104 and signal assignment section 106.The NCT-MIB contains the resource allocation information indicating theresources forming an EPDCCH CSS. For example, when type 2 distributedallocation (may be referred to as “type 2 distributed VRB allocation”)for allocation from a virtual resource block (VRB) to a physicalresource block (PRB) is used as resource allocation for EPDCCH CSS, theresource allocation information for EPDCCH CSS is information foridentifying the start position of and the number of contiguous RBs towhich the EPDCCH CSS is mapped. In addition, each bandwidth isconfigured with different values each serving as a candidate for thenumber of RBs to which an EPDCCH CSS is mapped. In addition, the numberof RBs to which the EPDCCH CSS is mapped can be selected from among thecandidates. For example, the larger the bandwidth is, the larger thenumber of RBs to which an EPDCCH CSS is mapped is. In addition, theNCT-MIB is subjected to scrambling processing based on the cell ID ofbase station 100.

Discovery signal generating section 102 generates a discovery signalbased on the cell ID of base station 100 and outputs the generateddiscovery signal to signal assignment section 106.

Common control signal generating section 103 generates DCIs (commoncontrol signals) to be transmitted using an EPDCCH CSS and outputs thegenerated DCIs to signal assignment section 106. The DCIs are controlsignals on the system information, paging, RACH, and transmission powercontrol and are masked with SI-RNTI, P-RNTI, RA-RNTI, and TPC-RNTI,respectively.

Error correction coding section 104 performs error correction coding ontransmission data signal (i.e., downlink data), and the controlinformation received from master information generating section 101 andoutputs the coded signal to modulation section 105.

Modulation section 105 modulates the signal received from errorcorrection coding section 104 and outputs the modulation signal tosignal assignment section 106.

Signal assignment section 106 assigns the common control signal receivedfrom common control signal generating section 103 to a resource in theEPDCCH CSS on the basis of the control information received from masterinformation generating section 101. Specifically, signal assignmentsection 106 identifies the RBs forming the EPDCCH CSS indicated by thecontrol information received from master information generating section101 and thereby assigns the common control signal to any of theidentified RBs. In addition, signal assignment section 106 assigns themodulation signal received from modulation section 105 to apre-configured downlink resource. Signal assignment section 106 alsoassigns the discovery signal received from discovery signal generatingsection 102 to a downlink resource based on the cell ID.

As described above, a transmission signal is generated by assigning thesignal including the downlink data and control information (NCT-MIB), adiscovery signal, or the common control signal assigned in the EPDCCHCSS to a predetermined resource. The generated transmission signal isoutputted to transmitting section 107.

Transmitting section 107 performs predetermined transmission processingsuch as up-conversion on the transmission signal received from signalassignment section 106 and transmits the processed signal to terminal200 via an antenna.

Receiving section 108 receives, via an antenna, a signal transmittedfrom terminal 200 and performs predetermined reception processing suchas down-conversion on the received signal. Receiving section 108 outputsthe processed signal to demodulation section 109.

Demodulation section 109 performs demodulation processing on the signalreceived from receiving section 108 and outputs the obtaineddemodulation signal to error correction decoding section 110.

Error correction decoding section 110 decodes the demodulation signalreceived from demodulation section 109 to acquire the received datasignal (i.e., uplink data).

[Configuration of Terminal 200]

FIG. 5 is a block diagram illustrating a configuration of terminal 200according to the present embodiment.

Referring to FIG. 5, terminal 200 includes receiving section 201, signaldemultiplexing section 202, demodulation section 203, error correctiondecoding section 204, discovery signal detecting section 205, masterinformation receiving section 206, common control signal receivingsection 207, error correction coding section 208, modulation section209, signal assignment section 210, and transmitting section 211.

Receiving section 201 receives, via an antenna, a signal transmittedfrom base station 100, then performs predetermined reception processingsuch as down-conversion on the received signal and outputs the processedsignal to signal demultiplexing section 202. Note that, the receivedsignal includes a signal including downlink data and control information(NCT-MIB), a discovery signal, or a common control signal, for example.

Signal demultiplexing section 202 extracts a signal corresponding to adata resource (downlink data and control information) from the receivedsignal and outputs the extracted signal to demodulation section 203. Inaddition, signal demultiplexing section 202 demultiplexes a resourcethat may include a discovery signal from the received signal and outputsthe components of the demultiplexed resource to discovery signaldetecting section 205. Moreover, signal demultiplexing section 202demultiplexes an EPDCCH CSS resource from the received signal receivedfrom receiving section 201, on the basis of resource allocationinformation for EPDCCH CSS received from master information receivingsection 206 to be described hereinafter, and outputs the components ofthe demultiplexed resource to common control signal receiving section207.

Demodulation section 203 demodulates the signal received from signaldemultiplexing section 202 and outputs the demodulated signal to errorcorrection decoding section 204.

Error correction decoding section 204 decodes the demodulation signalreceived from demodulation section 203 and outputs the acquired receiveddata signal. In addition, error correction decoding section 204 outputsthe acquired NCT-MIB to master information receiving section 206.

Discovery signal detecting section 205 detects a discovery signalindicating the cell ID of base station 100 from the received signal.Specifically, discovery signal detecting section 205 detects whether ornot a discovery signal is transmitted, using the signal received fromsignal demultiplexing section 202. When a discovery signal istransmitted, discovery signal detecting section 205 identifies the cellID by using the detected discovery signal. Discovery signal detectingsection 205 outputs the identified cell ID to master informationreceiving section 206.

Master information receiving section 206 extracts the resourceallocation information indicating the resources forming the EPDCCH CSSfrom the received signal, using the cell ID of base station 100.Specifically, master information receiving section 206 demodulates anNCT-MIB (NCT-MIB scrambled with cell ID) received from error correctiondecoding section 204, using the cell ID received from discovery signaldetecting section 205, and extracts the resource allocation informationfor EPDCCH CSS. Master information receiving section 206 outputs theresource allocation information for EPDCCH CSS to signal demultiplexingsection 202.

Common control signal receiving section 207 extracts a common controlsignal (DCI) from the received signal by performing blind-decoding withrespect to the EPDCCH CSS. Specifically, common control signal receivingsection 207 performs blind-decoding (i.e., monitoring) on the resourcesof the EPDCCH CSS received from signal demultiplexing section 202 andextracts a common control signal (DCI). Note that, each DCI is maskedwith SI-RNTI, P-RNTI, RA-RNTI, or TPC-RNTI.

Error correction coding section 208 performs error correction coding ona transmission data signal (uplink data) and outputs the coded signal tomodulation section 209.

Modulation section 209 modulates the signal outputted from errorcorrection coding section 208 and outputs the modulation signal tosignal assignment section 210.

Signal assignment section 210 assigns the signal received frommodulation section 209 to an uplink resource. The assigned signal isoutputted to transmitting section 211 as a transmission signal.

Transmitting section 211 performs predetermined transmission processingsuch as up-conversion on the transmission signal received from signalassignment section 210 and transmits the processed signal via anantenna.

[Operations of Base Station 100 and Terminal 200]

The operations of base station 100 and terminal 200 each configured inthe manner described above will be described in detail.

First of all, type 2 distributed allocation in LTE-Advanced will bedescribed.

In type 2 distributed allocation, the mapping rule from VRBs to PRBs isdefined in such a way that VRBs are allocated contiguously and that PRBsare distributedly allocated during mapping from VRBs to PRBs. Thestarting number of and the number of contiguously allocated VRBs arespecified as resource allocation information. As a result, the number ofbits required to indicate resource allocation can be kept small whilethe frequency diversity effect can be obtained in the meantime.Furthermore, in type 2 distributed allocation in LTE-Advanced, a mappingrule to be used varies between the first and second slots forming onesubframe, in order that VRBs mapped to PRBs vary between the first andsecond slots. As a result, the frequency diversity effect is furtherobtained. In addition, when DCI format 1C is used to indicate resourceallocation, the numbers that can be specified as the starting number ofVRBs are limited in order to further reduce the number of bits requiredto indicate resource allocation. Specifically, the starting number ofVRBs is selectable from 0, step, 2*step, 3*step, . . . Note that thevalue of step varies for each bandwidth. For example, step=2 when thenumber of RBs of the bandwidth is less than 50, and step=4 when thenumber of RBs of the bandwidth is 50 or greater.

Next, a method of indicating resource allocation information for EPDCCHCSS according to the present embodiment will be described.

In Embodiment 1, a method based on the type 2 distributed allocationdescribed above is used for indicating the resource allocation forEPDCCH CSS. Specifically, base station 100 indicates, to terminal 200,resource allocation information for identifying the starting number(start position) of and the number of contiguous VRBs to which an EPDCCHCSS is mapped. During this process, base station 100 indicates toterminal 200, using an NCT-MIB, the starting number (start position) ofand the number of contiguous VRBs for identifying the EPDCCH CSS.

In the current MIB specification, the following are configured: downlinkbandwidth (dl Bandwidth), PHICH mapping information (phich Config.(3bits)), the frame number used to transmit an MIB (systemFrame Number(8bits)), and a spare region for a functional expansion (spare.(10bits)).

MasterInformationBlock :: =SEQUENCE { dl Bandwidth ENUMERATED { n6, n15,n25, n50, n75, n100}, phich Config PHICH Config, systemFrameNumber BITSTRING (SIZE(8)), spare BIT STRING (SIZE(10)) }

Meanwhile, it is likely that no PHICH is used in NCT because NCTincludes no region in which a PDCCH is mapped, (see FIG. 1B). As aresult, a phich Config (and spare) region is can be used for indicatingother information in an NCT-MIB according to the current MIBspecification.

Accordingly, base station 100 indicates, to terminal 200, resourceallocation information indicating the starting number of and the numberof VRBs forming an EPDCCH CSS, using an NCT-MIB (e.g., phich Config andspare regions) in this embodiment. This NCT-MIB is scrambled with thecell ID of base station 100.

After acquisition of the cell ID of base station 100 by using adiscovery signal, terminal 200 receives the NCT-MIB and therebyidentifies the starting number of and the number of VRBs forming theEPDCCH CSS. In this manner, terminal 200 (e.g., idle mode UE) canrecognize base station 100 (e.g., small cell using S-NCT), then acquirethe resources (RB start position and the number of RBs) to which theEPDCCH CSS is mapped, and thus receive DCIs assigned in the EPDCCH CSS,without using a UE-specific control signal.

Regarding the resources of EPDCCH CSS to be indicated by using anNCT-MIB, in Embodiment 1, the starting number of VRBs forming the EPDCCHCSS is configured in the same method as the above described method usedin LTE-Advanced, for example. Specifically, the starting number of VRBsis selected from among 0, step, 2*step, 3*step, . . .

Meanwhile, the number of VRBs forming an EPDCCH CSS is configured byusing a method different from the above described method used inLTE-Advanced. Specifically, a larger number of VRBs (the number of PRBs)to which an EPDCCH CSS is mapped is configured for a larger downlinkbandwidth.

Setting a larger number of resources forming an EPDCCH CSS results in adecrease in the number of resources allocatable to a physical downlinkshared channel (i.e., data region, “PDSCH”) although the frequencydiversity effect improves in this case. A smaller number of resourcesallocatable to a PDSCH results in degradation of the downlinkthroughput. With this taken into consideration, however, the adverseeffect of degradation of the downlink throughput due to the limitationon the PDSCH is expected to be small in case of a larger bandwidth,while the effect of improvement in the throughput because of the qualityimprovement in the EPDCCH attributable to an increase in the number ofresources for the EPDCCH CSS is expected to be large. Thus, it iseffective to change the number of resources forming an EPDCCH CSS inaccordance with the bandwidth.

However, the number of resources (RBs) required to satisfy the qualityof EPDCCH CSS varies depending on the cell radius of the small cell orinterference or the like from a different cell. With this taken intoconsideration, a plurality of candidates for the number of RBs may beassociated with each bandwidth in this embodiment. FIG. 6 illustrates anexample of a correspondence between the number of RBs (N_RB)corresponding to the frequency bandwidth ([MHz]) and the number of RBsof EPDCCH CSS. As illustrated in FIG. 6, the larger the frequencybandwidth (the larger the number of N_RB) is, the larger the number ofRBs of EPDCCH CSS is configured. In addition, as illustrated in FIG. 6,two candidates for the number of RBs of EPDCCH CSS are associated witheach of the frequency bandwidths. In this case, base station 100 mayindicate, using one bit of an NCT-MIB (e.g., phich Config or spare), theinformation indicating which one of the plurality of candidates for thenumber of RBs as illustrated in FIG. 6 is used, as the resourceallocation information.

FIG. 7 illustrates a mapping example of an EPDCCH CSS. FIG. 7illustrates a mapping rule from VRBs to PRBs when the number of RBs ofthe entire band is 25. Specifically, as illustrated in FIG. 7, VRB #0 to#23 in ascending order are associated with PRB #0 to #23 in aninterleaved order.

When the number of RBs of the entire band is 25 (N_RB=25), any one of 2and 4 is configured as the number of RBs of EPDCCH CSS with reference toFIG. 6, for example. Let us consider a case where 4 is selected as thenumber of RBs of EPDCCH CSS, and the start position of the VRBs to whichthe EPDCCH CSS is mapped is VRB #8, for example. In this case, asillustrated in FIG. 7, the EPDCCH CSS is mapped to VRB #8, 9, 10, and 11in VRBs and PRB #9, 13, 17, and 21 in PRBs.

More specifically, in FIG. 7, base station 100 sets VRB #8 as the startposition and transmits, to terminal 200, an NCT-MIB containing resourceallocation information for the EPDCCH CSS consisting of 4 RBs, adiscovery signal indicating the cell ID used for the process ofscrambling the NCT-MIB, and a common control signal (DCI) assigned to aresource of the EPDCCH CSS consisting of PRB #9, 13, 17, and 21 (VRB #8,9, 10, and 11). Terminal 200 extracts the NCT-MIB using the cell IDindicated by the discovery signal, then identifies the EPDCCH CSSconsisting of PRB #9, 13, 17, and 21 (VRB #8, 9, 10, and 11) on thebasis of the resource allocation information contained in the NCT-MIB,and then receives the common control signal (DCI) by performingblind-decoding with respect to the EPDCCH CSS.

In Embodiment 1, in base station 100 (small cell) configured to use acarrier configuration which includes no PDCCH region and in which anEPDCCH is mapped in a data region, master information generating section101 generates resource allocation information indicating the resourcesforming an EPDCCH CSS and being scrambled with the cell ID of basestation 100 (i.e., NCT-MIB); and transmitting section 107 transmits theabove described resource allocation information, a discovery signalindicating the cell ID, and a common control signal (DCI) assigned inthe EPDCCH CSS, in the manner described above. Meanwhile, in terminal200, discovery signal detecting section 205 detects a discovery signalfrom the received signal that has been transmitted from base station100; and master information receiving section 206 extracts the resourceallocation information indicating the resources forming the EPDCCH CSSfrom the received signal by using the cell ID; and common control signalreceiving section 207 extracts a common control signal (DCI) from thereceived signal by performing blind-decoding with respect to the EPDCCHCSS.

Stated differently, according to the present invention, an idle mode UE(terminal 200) receives an NCT-MIB based on the cell ID identified bydetecting the discovery signal and thus can receive a DCI in the EPDCCHCSS identified on the basis of resource allocation information containedin the NCT-MIB. Specifically, according to the present embodiment,terminal 200 can recognize an EPDCCH CSS without a UE-specific controlsignal and acquire a DCI assigned in the EPDCCH CSS. As a result, evenin a small cell using S-NCT, an idle mode UE can recognize the smallcell and thereby receive DCIs on the system information, paging, andRACH as in BCT.

Moreover, according to the present embodiment, a larger number of RBs ofEPDCCH CSS is configured for a larger frequency bandwidth (larger numberof RBs of band). As a result, in case of a larger frequency bandwidth,the effect of improvement in the throughput because of the qualityimprovement in the EPDCCH can be obtained while the adverse effect ofdegradation of the downlink throughput due to the limitation on a PDSCHis kept small.

Note that, in this embodiment, the number of “steps” each used tospecify the start position of VRBs forming an EPDCCH CSS may beconfigured to have the same value as the number of sets of RBs of EPDCCHCSS. With this configuration, it is possible to secure the number ofcandidates for mapping an EPDCCH CSS for the number of sets of RBs thatenable mapping of an EPDCCH CSS without any overlapping between RBs inthe entire band.

Furthermore, although a mapping rule to be used varies between the firstand second slots in type 2 distributed allocation in LTE-Advanced, thesame mapping rule may be used in the first and second slots inEmbodiment 1. With this configuration, an EPDCCH CSS is mapped to thesame PRBs in the slots. This configuration is advantageous because sincea DMRS is used to demodulate an EPDCCH, it is better to map an EPDCCHCSS to the same PRBs in the first and second slots in order for theEPDCCH to be demodulated by using both DMRSes in the first and secondslots. In addition, using the same PRB number for mapping an EPDCCH CSSin the first and second slots can reduce the number of RBs that cannotbe used for PDSCH. In addition, although Embodiment 1 has been describedregarding a case where the rule (see FIG. 7) in the first slot isapplied as a mapping rule from VRBs to PRBs, a rule in the second slotmay be used.

In addition, in this embodiment, the period of CSS, which indicates howoften an EPDCCH CSS is transmitted, may be added as the resourceallocation information indicated by using an NCT-MIB. For example, it ispossible to allow the subframe period of mapping an EPDCCH CSS to beselected from among four types of subframe periods (5 msec, 10 msec, 20msec, and 40 msec), using two bits of the NCT-MIB. With thisconfiguration, the overhead amount of EPDCCH CSS is made adjustable inaccordance with the downlink traffic volume. Moreover, indicating asubframe in which no EPDCCH CSS is mapped can reduce misdetection andfalse detection of EPDCCH in terminal 200.

(Variation 1)

Although Embodiment 1 has been described regarding a case where thenumber of RBs used for an EPDCCH CSS is changed for each frequencybandwidth (the number of RBs) (see FIG. 6), the number of EPDCCHs to bemonitored by terminal 200 may be changed for each number of RBs used forEPDCCH and for each aggregation level (AL) to be described, hereinafter.

In LTE-Advanced, one RB consists of 12 subcarriers in the frequencydomain and has a width of 0.5 msec in the time domain. Two RBs combinedin the time domain are referred to as an RB pair as a unit.Specifically, an RB pair consists of 12 subcarriers in the frequencydomain and has a width of 1 msec in the time domain. Meanwhile, when anRB pair represents a group of 12 subcarriers in the frequency domain,the RB pair may be simply called “RB.” Moreover, in the physical layer,an RB pair is called a physical RB (PRB) pair. In addition, a unitdefined by one subcarrier and one OFDM symbol is called a resourceelement (RE).

In an EPDCCH, resource units each called “enhanced resource elementgroup (EREG)” are formed by dividing each PRB pair into 16 resources,and a resource unit consists of 4 or 8 EREGs is called “enhanced controlchannel element (ECCE).” In addition, the number of ECCEs forming anEPDCCH transmitting one control signal is called “aggregation level.” AnEPDCCH has a plurality of aggregation levels. Each aggregation level haspre-defined EPDCCH candidates. The term “EPDCCH candidate” refers to acandidate for a region to which a control signal is assigned, and asearch space consists of a plurality of EPDCCH candidates. For example,the number of PDCCH candidates for a PDCCH CSS is 4 in aggregation level4 (AL4) and 2 in aggregation level 8 (AL8).

For example, when one ECCE consists of 4 EREGs in an EPDCCH, the numberof ECCEs is 32 for 8 RBs (i.e., the number of PRB pairs) and the numberof ECCEs is 16 for 4 RBs. Moreover, the number of ECCEs is 8 for 2 RBsand the number of ECCEs is 4 for 1 RB in this case. Accordingly, whenthe number of EPDCCH candidates for EPDCCH CSS is 4 in AL4 and 2 in AL8as in the case of PDCCH CSS, ECCEs forming each EPDCCH candidateoverlap.

For this reason, the AL of EPDCCH CSS may be changed for each number ofRBs forming the EPDCCH CSS in order to avoid overlapping of EPDCCHcandidates for the EPDCCH CSS. For example, FIG. 8 illustrates acorrespondence between the number of RBs used for EPDCCH CSS, theaggregation level (AL) and the number of EPDCCHs to be monitored byterminal 200. Note that, FIG. 8 illustrates a case where one ECCEconsists of 4 EREGs in an EPDCCH.

As illustrated in FIG. 8, the number of EPDCCH candidates for EPDCCH CSSis configured to be 3 for AL1, 2 for AL2, and 1 for AL4 when the numberof RBs for EPDCCH CSS is 1 (the number of ECCEs: 4). The number ofEPDCCH candidates for EPDCCH CSS is configured to be 3 for AL2, 2 forAL4, and 1 for AL8 when the number of RBs for EPDCCH CSS is 2 (thenumber of ECCEs: 8) in FIG. 8. In addition, when the number of RBs forEPDCCH CSS is 4 (the number of ECCEs: 16), the number of EPDCCHcandidates for EPDCCH CSS is configured to be 4 for AL4, and 2 for AL8in FIG. 8. When the number of RBs for EPDCCH CSS is 8 (the number ofECCEs: 32), the number of EPDCCH candidates for EPDCCH CSS is configuredto be 3 for AL4, 2 for AL8, and 1 for AL16 in FIG. 8.

With this configuration, EPDCCH candidates in each aggregation level canbe configured without overlapping of ECCEs.

(Variation 2)

Embodiment 1 has been described regarding a case where the startposition of VRBs for EPDCCH CSS is indicated by an NCT-MIB. However, inVariation 2, the start position of VRBs for EPDCCH CSS is specified onthe basis of the cell ID. In this case, the resource allocationinformation contained in the NCT-MIB becomes information that indicatesonly the number of VRBs forming the EPDCCH CSS. With this configuration,the number of bits required to indicate the resource allocation forEPDCCH CSS can be further reduced compared with the present embodimentdescribed above. In this configuration, the cell ID is acquired from adiscovery signal in terminal 200, for example. The term “cell ID” isalso referred to as “physical cell ID (PCID).”

The start position of RBs (RB_start) based on the cell ID is calculatedin accordance with equation 1 below, for example.

[1]

RB_start=(PCID mod floor(N_VRB/K))*K  (Equation 1)

In equation 1, K represents the number of RBs allocated to the EPDCCHCSS, and N_VRB represents the number of VRBs in total. For example,where PCID=1500, K=4, and N_VRB=24, RB_start=(1500 mod floor 24/4)*4=0.As a result, the EPDCCH CSS is assigned to VRB #0, 1, 2, and 3 in VRBsand PRB #0, 4, 8, and 12 in PRBs (see FIG. 9, for example).

However, if the start position of RBs for EPDCCH CSS overlaps betweenneighboring cells, interference occurs between the cells. In order toavoid such interference between the neighboring cells, a shift value maybe configured in this case. For example, setting an integral multiple ofK as the shift value makes it possible to avoid overlapping of EPDCCHCSS between neighboring cells in all RBs. Regarding the shifting of RBstart position, one shift value may be pre-defined, and the presence orabsence of shifting of the start position of RBs may be indicated byusing one bit. In addition, it is also possible to use two or more bitsto allow the shift value to be selected from among a plurality of shiftvalues.

Note that, since K is used to represent the number of RBs allocated toan EPDCCH CSS in equation 1, the number of candidates for the number ofsets that enable mapping without any overlapping between EPDCCH CSSescan be secured in the entire band. When overlapping is allowed, K may beused to represent half of the number of RBs allocated to an EPDCCH CSS.

Embodiment 2

In Embodiment 2, a method of avoiding a collision between a discoverysignal (or synchronization signal) and an EPDCCH CSS will be described.

In Embodiment 2, it is assumed that a discovery signal is mapped to aspecific resource element (RE) in a subframe and also that UEs are madeaware of the mapping position of the discovery signal in advance.

[Configuration of Base Station 300]

FIG. 10 is a block diagram illustrating a configuration of base station300 according to Embodiment 2 of the present invention. In FIG. 10, thesame components as those illustrated in Embodiment 1 (FIG. 4) areassigned the same reference numerals and redundant descriptions of thecomponents will be omitted hereinafter.

In FIG. 10, as in Embodiment 1 (signal assignment section 106), signalassignment section 301 assigns a modulation signal received frommodulation section 105, a common control signal received from commoncontrol signal generating section 103, and a discovery signal receivedfrom discovery signal generating section 102 to corresponding resources,respectively. During the assignment, when a resource to which an EPDCCHCSS is mapped and a resource to which the discovery signal is mappedcollide with each other, signal assignment section 301 changes theresource to which the EPDCCH CSS is mapped. Note that, the method ofchanging a mapping resource for EPDCCH CSS will be described,hereinafter.

[Configuration of Terminal 400]

FIG. 11 is a block diagram illustrating a configuration of terminal 400according to Embodiment 2 of the present invention. Note that, in FIG.11, the same components as those illustrated in Embodiment 1 (FIG. 5)are assigned the same reference numerals, and redundant descriptions ofthe components are omitted, hereinafter.

Referring to FIG. 11, discovery signal detecting section 401 performsthe operations described in Embodiment 1 (i.e., discovery signaldetecting section 205) and also outputs the transmission period of adiscovery signal, and resource information (e.g., mapping position) tosignal demultiplexing section 402.

As in Embodiment 1 (signal demultiplexing section 202), signaldemultiplexing section 402 demultiplexes, from the received signal, asignal corresponding to a data resource (i.e., downlink data and controlinformation), a resource that may include a discovery signal, and aresource for EPDCCH CSS. During this processing, signal demultiplexingsection 402 recognizes a resource that may involve a collision between aresource to which a discovery signal is mapped and a resource to whichan EPDCCH CSS is mapped, on the basis of the transmission period of adiscovery signal, and the resource information received from discoverysignal detecting section 401 and the resource allocation information forthe EPDCCH CSS received from master information receiving section 206.Signal demultiplexing section 402 recognizes that there has been achange in resources to which the EPDCCH CSS is mapped, for a resourcethat may involve a collision, and thus demultiplexes the components ofthe resources for EPDCCH CSS from the received signal. Note that, themethod of changing a mapping resource for EPDCCH CSS will be described,hereinafter.

[Operations of Base Station 300 and Terminal 400]

The operations of base station 300 and terminal 400 each configured inthe manner described above will be described in detail.

Operation Examples 1 to 3 will be described with respect to the methodof changing a mapping resource for EPDCCH CSS in base station 300 andterminal 400.

Operation Example 1

In Operation Example 1, when a pattern in which a discovery signal andEPDCCH CSS are mapped in the same subframe is used, no EPDCCH CSS ismapped in this subframe. Specifically, a collision between a discoverysignal and EPDCCH CSS is avoided on a per-subframe basis in OperationExample 1.

For example, as illustrated in FIG. 12, it is assumed that thetransmission interval of a discovery signal is 5 msec (e.g., subframe #N-10, # N-5, # N, # N+5, # N+10), and that the transmission interval ofan EPDCCH CSS is 2 msec (e.g., subframe # N-4, # N-2, # N, # N+2, #N+4). In this case, transmission timing at which a discovery signal andEPDCCH CSS are mapped in the same subframe and thus collide with eachother corresponds to the interval of 10 msec (e.g., subframe # N-20, #N-10, # N, # N+10, # N+20).

In this operation, terminal 400 detects a discovery signal, thenreceives an MIB using the discovery signal, and identifies the EPDCCHCSS. For this reason, it is favorable for terminal 400 to receive adiscovery signal preferentially over an EPDCCH CSS.

In this respect, base station 300 (signal assignment section 301) mapsno EPDCCH CSS (i.e., transmits no EPDCCH CSS) in subframes transmittedat the intervals of 10 msec, which correspond to the transmission timingof a discovery signal (e.g., subframe # N in FIG. 12) among thesubframes corresponding to the transmission timing of EPDCCH CSS.Likewise, terminal 400 (signal demultiplexing section 402) skips theprocess of detecting an EPDCCH CSS in subframes transmitted at theintervals of 10 msec, which correspond to the transmission timing of adiscovery signal (e.g., subframe # N in FIG. 12) among the subframescorresponding to the transmission timing of EPDCCH CSS. Terminal 400(signal demultiplexing section 402) in this case does not perform theoutput processing to common control signal receiving section 208 in thiscase.

With this configuration, no EPDCCH CSS is mapped in a subframe in whicha discovery signal is mapped among a plurality of subframes eachpre-configured as a subframe in which an EPDCCH CSS is to be mapped. Asa result, performing the transmission and reception of a discoverysignal preferentially over the transmission and reception of an EPDCCHCSS makes it possible to keep the detection accuracy of cells. Inaddition, avoiding simultaneous transmission of a discovery signal andEPDCCH CSS makes it possible to keep the quality of EPDCCH CSS, so thatthe probability of false detection and misdetection of an EPDCCH CSS canbe kept low.

Note that, when the transmission interval of EPDCCH CSS is variable, thetransmission interval of EPDCCH CSS may be determined taking intoconsideration the resource amount required for EPDCCH CSS and acollision with a discovery signal.

Operation Example 2

In Operation Example 2, when a pattern in which a discovery signal andEPDCCH CSS are mapped in the same subframe is used, an EPDCCH CSS ismapped to a resource (RE) while avoiding a resource (RE) to which adiscovery signal is mapped in this subframe. Specifically, a collisionbetween a discovery signal and EPDCCH CSS is avoided on a per-RE basisin Operation Example 2.

As illustrated in FIG. 13, as in Operation Example 1, it is assumed thatthe transmission interval of a discovery signal is 5 msec (e.g.,subframe # N-10, # N-5, # N, # N+5, # N+10), and that the transmissioninterval of an EPDCCH CSS is 2 msec (e.g., subframe # N-4, # N-2, # N, #N+2, # N+4), for example. In this case, transmission timing at which adiscovery signal and EPDCCH CSS are mapped in the same subframe and thuscollide with each other corresponds to the interval of 10 msec (e.g.,subframe # N-20, # N-10, # N, # N+10, # N+20).

For this reason, base station 300 (signal assignment section 301)assigns a common control signal (DCI) to a resource other than aresource (RE) to which a discovery signal is mapped among the resourcesindicated by the resource allocation information, at the timing when adiscovery signal and EPDCCH CSS are mapped in the same subframe.Specifically, base station 300 assigns no common control signal (DCI) toa resource for EPDCCH CSS, which overlaps with a resource (RE) used formapping a discovery signal, at the timing when a discovery signal andEPDCCH CSS are mapped in the same subframe. Likewise, terminal 400(signal demulitplexing section 402 and common control signal receivingsection 207) demultiplex the resources other than the resource (RE) towhich the discovery signal is mapped from the resources indicated by theresource allocation information, at the timing when a discovery signaland EPDCCH CSS are mapped in the same subframe, and acquires a commoncontrol signal (DCT) by blindly decoding the demultiplexed resources.

As described above, in a subframe in which a discovery signal and EPDCCHCSS are both to be mapped, an EPDCCH CSS is mapped to a resource otherthan a resource to which a discovery signal is mapped, among theresources indicated by the resource allocation information. With thisconfiguration, the characteristics of EPDCCH CSS may degrade unfavorablyby the amount of reduction in the number of resources for EPDCCH CSS.However, if the radio quality with terminal 400 can be estimated byusing RACH response and/or the like, base station 300 can reduce thedegradation of characteristics of the EPDCCH CSS by using a subframe inwhich a discovery signal and EPDCCH CSS are to be mapped, for terminal400 having favorable radio quality with base station 300.

Meanwhile, using a high aggregation level results in reduction in thetotal amount of DCI to be transmitted on the EPDCCH CSS, but makes itpossible to secure the quality of EPDCCH CSS. Accordingly, thelimitation on the number of resources used for EPDCCH CSS in thesubframe in which a discovery signal and EPDCCH CSS are mapped can bereduced.

In addition, since terminal 400 recognizes the resource (RE) to which adiscovery signal is mapped in the cell, terminal 400 can recognize thatthe resource for an EPDCCH CSS planned to be mapped to the RE has beensubjected to puncturing or rate matching. Note that, the term“puncturing” herein refers to skipping reception of the RE to which adiscovery signal is mapped while the mapping sequence of resourcesremains the same. The term “rate matching” used herein refers to atechnique that changes coding in accordance with the number of availableREs.

Moreover, as in Operation Example 1, preferentially transmitting adiscovery signal over an EPDCCH CSS makes it possible to keep thedetection accuracy of cells. In addition, avoiding transmission of adiscovery signal and EPDCCH CSS using the same resource makes itpossible to keep the quality of EPDCCH CSS, which in turn makes itpossible to prevent the probability of false detection and misdetectionof an EPDCCH CSS from increasing.

Operation Example 3

In Operation Example 3, when a pattern in which a discovery signal andEPDCCH CSS are mapped in the same subframe is used, an EPDCCH CSS ismapped to a resource (RE) while avoiding a resource (RE) to which adiscovery signal is mapped in the subframe as in Operation Example 2.

In Operation Example 2, no EPDCCH CSS is mapped to the resource to whicha discovery signal is mapped in the subframe, resulting in reduction inthe number of RBs for EPDCCH CSS, however. For this reason, in OperationExample 3, in order to secure the number of RBs for EPDCCH CSS, aresource to which the EPDCCH CSS is mapped (e.g., VRB) is shifted by thenumber of RBs which cause a collision between a discovery signal andEPDCCH CSS. Operation Example 3 is effective particularly when the RBsto which a discovery signal is mapped are limited as in the case ofPSS/SSS.

Specifically, base station 300 maps an EPDCCH CSS while shifting aresource (RB) to which the EPDCCH CSS is mapped in order to avoid acollision between a discovery signal and EPDCCH CSS at the timing when adiscovery signal and EPDCCH CSS are mapped in the same subframe.Meanwhile, terminal 400 recognizes that an EPDCCH CSS is mapped so as toavoid a collision between a discovery signal and EPDCCH CSS at thetiming when a discovery signal and EPDCCH CSS are mapped in the samesubframe, and then identifies the EPDCCH CSS.

A description will be provided regarding a case where the number of RBsof the band is 25, and a discovery signal is mapped to a center portionof the band as in the case of a PSS/SSS as illustrated in FIG. 14. InFIG. 14, the discovery signal is mapped to PRB #9, 10, 11, 12, 13, 14,and 15 (substantially the center of band). In addition, as the resourceallocation information for the EPDCCH CSS, the start position of VRBs isassumed to be VRB #8 and the number of VRBs is assumed to be 4.

In this case, when an EPDCCH CSS is mapped to 4 VRBs of VRB #8 to #11 asin Embodiment 1 (FIG. 7), the discovery signal and EPDCCH CSS collidewith each other at VRB #8 and #9, i.e., PRB #9 and #13. In order toavoid a collision, two VRBs of VRB #8 and #9, where the discovery signaland EPDCCH CSS collide with each other are skipped in allocation of VRBsfor the EPDCCH CSS in Operation Example 3. As a result, the EPDCCH CSSis mapped to VRB #10 to #13 in Operation Example 3. In other words, theresources to which the EPDCCH CSS is mapped become VRB #10 to #13 byshifting VRB #8 to #11 indicated by the resource allocation informationby two VRBs. Accordingly, 4 VRBs are secured as the resources for EPDCCHCSS.

As described above, in a subframe in which a discovery signal is mappedamong a plurality of subframes each pre-configured as a subframe inwhich an EPDCCH CSS is to be mapped, the EPDCCH CSS is mapped to aresource other than the resource to which a discovery signal is mapped,by skipping a resource that overlaps with a resource (RE) to which adiscovery signal is mapped among the resources indicated by the resourceallocation information. As a result, while the resources for EPDCCH CSSare secured (without any reduction in the number of resources for EPDCCHCSS), a collision between a discovery signal and EPDCCH CSS can beavoided as illustrated in FIG. 15. Stated differently, according toOperation Example 3, it is possible to keep the detection accuracy ofcells while keeping the quality of EPDCCH CSS. Thus, the probability offalse detection and misdetection of an EPDCCH CSS can be kept low.

Next, a description will be provided with reference to FIG. 16 regardinga case where the number of RBs of the band is 50, for example.

In this example, it is assumed that a discovery signal is mapped to PRB#22, 23, 24, 25, 26, and 27 at a center portion of the band as in thecase of a PSS/SSS. In addition, when the number of RBs of the band is50, the number of VRBs is 46 (VRB #0 to #45). In addition, when thenumber of RBs of the band is 50, “step” indicating the start position ofthe VRBs is 4, and the candidates for the start position of VRBs are 11in total, including VRB #0, 4, 8, . . . 40. For example, when the numberof RBs for EPDCCH CSS is 4, 11 EPDCCH CSS mapping patterns (11 patternseach enclosed by a dotted line in FIG. 16) are configured as candidatesfor the resources forming an EPDCCH CSS. Specifically, any one of the 11patterns is specified as the EPDCCH CSS.

Among the 11 patterns each enclosed by a dotted line in FIG. 16, acollision with a discovery signal occurs in four patterns, however.

In order to avoid a collision, the EPDCCH CSS is mapped so as to avoid acollision with a discovery signal in Operation Example 3.

Specifically, as illustrated in FIG. 16, the candidates for the startposition of VRBs for EPDCCH CSS are configured to be VRB #0, 4, 9, 13,17, 22, 26, 32, 36, and 42, and 4 RBs are configured as a single patternwhich is a candidate for the resources forming an EPDCCH CSS, while theresources to which a discovery signal is mapped are avoided (i.e.,patterns each enclosed by a solid line in FIG. 16). In this case, 10EPDCCH CSS patterns which do not involve a collision with a discoverysignal can be secured. In addition, an EPDCCH CSS is mapped to differentRBs in the 10 patterns (no overlapping between RBs), so that a collisionof EPDCCH CSS can be avoided between cells in which a discovery signalis mapped to the same RBs.

For example, base station 300 may indicate the start position of and thenumber of RBs for EPDCCH CSS to terminal 400. Terminal 400 recognizes,as the resources for EPDCCH CSS, one pattern corresponding to the startposition of RBs from among a plurality of EPDCCH CSS patternscorresponding to the number of RBs for EPDCCH indicated by base station300 (e.g., patterns illustrated in FIG. 16 when the number of RBs is 4).Specifically, in FIG. 16, terminal 400 identifies any one of a pluralityof EPDCCH CSS patterns on the basis of the resource allocationinformation indicating the start position of and the number of RBsforming the EPDCCH CSS.

In the manner described above, a plurality of patterns which arecandidates for the resources forming an EPDCCH CSS are pre-configured.In addition, each of the plurality of patterns is formed of a resourceother than a resource to which a discovery signal is mapped. Inaddition, the resource allocation information for the EPDCCH CSS isinformation that identifies any one of the plurality of patterns.Accordingly, pre-configuring the resource mapping patterns for EPDCCHCSS by using the resources that do not involve a collision with adiscovery signal allows terminal 400 to receive DCIs in the EPDCCH CSSwithout taking into consideration a collision between a discovery signaland EPDCCH CSS.

Note that, the resource allocation information for EPDCCH CSS is notlimited to information indicating the start position of and the numberof RBs forming the EPDCCH CSS. For example, the resource allocationinformation for EPDCCH CSS may be information indicating a pattern to beused among a plurality of patterns.

In addition, although a description has been provided regarding a casewhere the number of RBs of the band is 50 as an example, the number ofRBs of the band is not limited to 50. For example, EPDCCH CSS patternsthat do not involve a collision with a discovery signal may bepre-configured for the number of RBs other than 50 (e.g., 6, 15, 25, 75,100 RBs).

Operation Examples 1 to 3 have been described above with respect to themethod of changing an EPDCCH CSS mapping resource in base station 300and terminal 400.

As described above, according to the present embodiment, a collisionbetween a discovery signal (or synchronization signal) and EPDCCH CSScan be avoided.

Note that, the present embodiment has been described with a case wheretype 2 distributed allocation (resource allocation information foridentifying the start position of and the number of RBs) is used toindicate the mapping position of an EPDCCH CSS, but the presentinvention is not limited to this case. For example, resource allocationinformation that identifies an RB or a group of RBs which correspond tothe mapping position of an EPDCCH CSS may be used.

Moreover, although the embodiment has been described with a case where acollision between an EPDCCH CSS and discovery signal is avoided, thisembodiment can be applied to a case where a collision between an EPDCCHCSS and NCT-MIB is avoided.

The embodiments of the present invention have been described above.

OTHER EMBODIMENTS

Note that, although the embodiments have been described above with acase where an EPDCCH CSS is mapped in NCT, the embodiments describedabove may be applied to a case where an EPDCCH CSS is mapped in BCT. Inparticular, in case of machine type communication (MTC) in whichexpansion of cell coverage is required, for example, when sufficientcell coverage cannot be secured using a CSS in a PDCCH, the cellcoverage can be expanded using an EPDCCH CSS.

In the above described embodiments, an EPDCCH CSS is described as a CSSdetectable based on the cell ID. In other words, the embodiments havebeen described regarding a case where one CSS is set in one cell.However, a plurality of CSSes may be configured in one cell while eachterminal is configured to select a specific CSS from the plurality ofCSSes. In this respect, a CSS used in the embodiments may be expanded insuch a way that a CSS is configured on a per-UE group basis (group CSSor UE group CSS). For example, a UE group CSS may be configured inenhancement for DL-UL interference management and traffic adaptation(eIMTA), coordinated of multiple point transmission and reception(CoMP), or NS-NCT. For example, while cell IDs are used in theembodiments described above, group IDs may be used for a case where agroup CSS is applied. For example, group IDs may be IDs each indicatinga group of a plurality of cells employing the same configuration ineIMTA, or may be IDs each indicating a group of a plurality of cellsoperating coordinately in CoMP. The group IDs in this case are indicatedto terminals by UE-specific higher layer signaling, for example.

The present invention has been described above by examples of hardwareimplementations in the above-noted embodiment, but the present inventioncan be also implemented by software in conjunction with hardware.

In addition, the functional blocks used in the description of theembodiments are typically implemented as LSI devices, which areintegrated circuits. The functional blocks may be formed as individualchips, or a part or all of the functional blocks may be integrated intoa single chip. Although the term “LSI” is used herein, the terms “IC,”“system LSI,” “super LSI” or “ultra LSI” may be used as well dependingon the level of integration.

In addition, the circuit integration is not limited to LSI and may beachieved by dedicated circuitry or a general-purpose processor otherthan an LSI. After fabrication of LSI, a field programmable gate array(FPGA), which is programmable, or a reconfigurable processor, whichallows reconfiguration of connections and settings of circuit cells inLSI may be used.

Should a circuit integration technology replacing LSI appear as a resultof advancements in semiconductor technology or other technologiesderived from the technology, the functional blocks could be integratedusing such a technology. Another possibility is the application ofbiotechnology and/or the like.

A base station apparatus according to the present disclosure is a basestation apparatus using a carrier configuration which includes no regionfor mapping a physical downlink control channel (PDCCH) and in which anenhanced physical downlink control channel (EPDCCH) is mapped in a dataregion, the base station apparatus including: a generating section thatgenerates allocation information indicating one or more resources whichform a search space in the EPDCCH and being scrambled with a cell ID ofthe base station apparatus; and a transmitting section that transmitsthe allocation information, a detection signal indicating the cell ID,and a control signal assigned in the search space.

In the base station apparatus according to the present disclosure, thesearch space is not mapped in a subframe in which the detection signalis mapped among a plurality of subframes each pre-configured as asubframe in which the search space is to be mapped.

In the base station apparatus according to the present disclosure, in asubframe in which the detection signal and the search space are both tobe mapped, the search space is mapped to a resource other than aresource to which the detection signal is mapped among the resourcesindicated by the allocation information.

In the base station apparatus according to the present disclosure, in asubframe in which the detection signal is mapped among a plurality ofsubframes each pre-configured as a subframe in which the search space isto be mapped, the search space is mapped to a resource other than aresource to which the detection signal is mapped, by skipping a resourcethat overlaps with the resource to which the detection signal is mappedamong the resources indicated by the allocation information.

In the base station apparatus according to the present disclosure: aplurality of patterns each being a candidate for one or more resourceswhich form the search space are pre-configured; each of the plurality ofpatterns is formed of a resource other than a resource to which thedetection signal is mapped; and the allocation information isinformation that identifies any one of the plurality of patterns.

In the base station apparatus according to the present disclosure: theallocation information is information that indicates a start position ofand the number of the resources which are consecutive and to which thesearch space is mapped; and the number of resources is larger for alarger downlink bandwidth.

In the base station apparatus according to the present disclosure: eachdownlink bandwidth is associated with a plurality of candidates for thenumber of resources; and the allocation information further includesinformation that indicates which one of the plurality of candidates isto be used.

In the base station apparatus according to the present disclosure: astart position of the resources which are consecutive and to which thesearch space is mapped is determined based on the cell ID; and theallocation information is information that indicates the number ofresources.

In the base station apparatus according to the present disclosure, theallocation information further includes information that indicates aperiod of mapping the search space.

A terminal apparatus according to the present disclosure includes: adetection section that detects a detection signal from a received signaltransmitted from a base station apparatus using a carrier configurationwhich includes no region for mapping a physical downlink control channel(PDCCH) and in which an enhanced physical downlink control channel(EPDCCH) is mapped in a data region, the detection signal indicating acell ID of the base station apparatus; a first receiving section thatextracts allocation information from the received signal, using the cellID, the allocation information indicating one or more resources whichform a search space in the EPDCCH; and a second receiving section thatextracts a control signal from the received signal by performingblind-decoding with respect to the search space.

A transmitting method according to the present disclosure is atransmitting method in a base station apparatus using a carrierconfiguration which includes no region for mapping a physical downlinkcontrol channel (PDCCH) and in which an enhanced physical downlinkcontrol channel (EPDCCH) is mapped in a data region, the transmittingmethod including: generating allocation information indicating one ormore resources which form a search space in the EPDCCH and beingscrambled with a cell ID of the base station apparatus; and transmittingthe allocation information, a detection signal indicating the cell ID,and a control signal assigned in the search space.

A receiving method according to the present disclosure includes:detecting a detection signal from a received signal transmitted from abase station apparatus using a carrier configuration which includes noregion for mapping a physical downlink control channel (PDCCH) and inwhich an enhanced physical downlink control channel (EPDCCH) is mappedin a data region, the detection signal indicating a cell ID of the basestation apparatus; extracting allocation information from the receivedsignal, using the cell ID, the allocation information indicating one ormore resources which form a search space in the EPDCCH; and extracting acontrol signal from the received signal by performing blind-decodingwith respect to the search space.

INDUSTRIAL APPLICABILITY

The present invention is suitable for use in mobile communicationsystems, for example.

REFERENCE SIGNS LIST

-   -   100, 300 Base station    -   200, 400 Terminal    -   101 Master information generating section    -   102 Discovery signal generating section    -   103 Common control signal generating section    -   104, 208 Error correction coding section    -   105, 209 Modulation section    -   106, 210, 301 Signal assignment section    -   107, 211 Transmitting section    -   108, 201 Receiving section    -   109, 203 Demodulation section    -   110, 204 Error correction decoding section    -   202, 402 Signal demultiplexing section    -   205, 401 Discovery signal detecting section    -   206 Master information receiving section    -   207 Common control signal receiving section

The various embodiments described above can be combined to providefurther embodiments. All of the U.S. patents, U.S. patent applicationpublications, U.S. patent applications, foreign patents, foreign patentapplications and non-patent publications referred to in thisspecification and/or listed in the Application Data Sheet areincorporated herein by reference, in their entirety. Aspects of theembodiments can be modified, if necessary to employ concepts of thevarious patents, applications and publications to provide yet furtherembodiments.

These and other changes can be made to the embodiments in light of theabove-detailed description. In general, in the following claims, theterms used should not be construed to limit the claims to the specificembodiments disclosed in the specification and the claims, but should beconstrued to include all possible embodiments along with the full scopeof equivalents to which such claims are entitled. Accordingly, theclaims are not limited by the disclosure.

1. An integrated circuit to control a process, the process comprising:receiving assignment information that is generated using bits other thanbits for a downlink bandwidth (dl bandwidth) and a frame number(systemFrameNumber) in a master information block (MIB); and decoding,based on the assignment information, a control channel on a data regionthat is different from a region where a physical downlink controlchannel is mapped, wherein information related to one or more of systeminformation, paging, and a random access channel (RACH) is included inthe control channel mapped on the data region and not in the physicaldownlink control channel.
 2. The integrated circuit according to claim1, comprising: circuitry which, in operation, controls the process; atleast one input coupled to the circuitry, wherein the at least oneinput, in operation, inputs data; and at least one output coupled to thecircuitry, wherein the at least one output, in operation, outputs data.3. The integrated circuit according to claim 1, wherein the controlchannel mapped on the data region is mapped on a search space, and theassignment information is related to a resource forming the searchspace.
 4. The integrated circuit according to claim 1, wherein theassignment information is scrambled by a cell identity (ID).
 5. Theintegrated circuit according to claim 1, wherein the control channelmapped on the data region is mapped in a subframe other than a subframeon which one of the MIB and a discovery signal for detecting a cell IDis mapped.
 6. The integrated circuit according to claim 1, wherein thecontrol channel mapped on the data region is mapped periodically.
 7. Theintegrated circuit according to claim 1, wherein the control channelmapped on the data region is masked with one of a system informationradio network temporary identifier (SI-RNTI), a paging RNTI (P-RNTI),and a random access RNTI (RA-RNTI).
 8. The integrated circuit accordingto claim 1, wherein the control channel mapped on the data region ismapped based on a cell ID.
 9. The integrated circuit according to claim8, wherein the process comprises receiving a discovery signal fordetecting the cell ID.
 10. The integrated circuit according to claim 1,wherein the control channel mapped on the data region is mapped in asearch space, which is determined based on a starting resource block anda number of consecutive resource blocks.
 11. The integrated circuitaccording to claim 10, wherein the starting resource block is determinedbased on a cell ID.
 12. The integrated circuit according to claim 1,wherein a number of control channels that are monitored depends on anumber of resource blocks forming a search space and an aggregationlevel.
 13. An integrated circuit comprising circuitry, which, inoperation: controls reception of assignment information that isgenerated using bits other than bits for a downlink bandwidth (dlbandwidth) and a frame number (systemFrameNumber) in a masterinformation block (MIB); and decodes, based on the assignmentinformation, a control channel on a data region that is different from aregion where a physical downlink control channel is mapped, whereininformation related to one or more of system information, paging, and arandom access channel (RACH) is included in the control channel mappedon the data region and not in the physical downlink control channel. 14.The integrated circuit according to claim 13, comprising: at least oneinput coupled to the circuitry, wherein the at least one input, inoperation, inputs data; and at least one output coupled to thecircuitry, wherein the at least one output, in operation, outputs data.15. The integrated circuit according to claim 13, wherein the controlchannel mapped on the data region is mapped on a search space, and theassignment information is related to a resource forming the searchspace.
 16. The integrated circuit according to claim 13, wherein theassignment information is scrambled by a cell identity (ID).
 17. Theintegrated circuit according to claim 13, wherein the control channelmapped on the data region is mapped in a subframe other than a subframeon which one of the MIB and a discovery signal for detecting a cell IDis mapped.
 18. The integrated circuit according to claim 13, wherein thecontrol channel mapped on the data region is mapped periodically. 19.The integrated circuit according to claim 13, wherein the controlchannel mapped on the data region is masked with one of a systeminformation radio network temporary identifier (SI-RNTI), a paging RNTI(P-RNTI), and a random access RNTI (RA-RNTI).
 20. The integrated circuitaccording to claim 13, wherein the control channel mapped on the dataregion is mapped based on a cell ID.
 21. The integrated circuitaccording to claim 20, wherein the circuitry, in operation, controlsreception of a discovery signal for detecting the cell ID.
 22. Theintegrated circuit according to claim 13, wherein the control channelmapped on the data region is mapped in a search space, which isdetermined based on a starting resource block and a number ofconsecutive resource blocks.
 23. The integrated circuit according toclaim 22, wherein the starting resource block is determined based on acell ID.
 24. The integrated circuit according to claim 13, wherein anumber of control channels that are monitored depends on a number ofresource blocks forming a search space and an aggregation level.